NBME Form 9 Practice Test

Abnormal placental attachment to the myometrium occurs when placental villi attach directly to the muscular wall of the uterus rather than being anchored in the decidua basalis. This is placenta accreta. It can exist on a spectrum where the villi invade the myometrium (increta) or even through it to surrounding organs (percreta) in more severe cases. The key idea is abnormal adhesion to the myometrium rather than proper separation at delivery, which can lead to heavy postpartum bleeding and retained placenta. Placenta previa describes a placenta implanted over the cervical opening, which can cause painless bleeding in pregnancy. Placental abruption is the premature separation of the placenta from the uterine wall, causing vaginal bleeding and abdominal pain. Vasa previa involves fetal blood vessels crossing the cervix, posing risk of fetal hemorrhage during rupture of membranes.